Combined FEM-reaction method for EMS analysis of a PCB in a low-Q enclosure

In this paper, a combined method based on the finite element method (FEM) and the reaction theorem, is proposed to analyze the electromagnetic susceptibility (EMS) of a printed circuit board (PCB) in a low-quality(Q) shielding enclosure. Here, we focus on the situation that an external incident electromagnetic interference (EMI) enters into an enclosure through aperture coupling, and further couples to the PCB inside the enclosure through board-edge coupling. The proposed method consists of three steps. Firstly, the incident fields inside the enclosure with the absence of the PCB are calculated by using the FEM. Then, the radiated fields of the PCB in the free space are also calculated by the FEM. Finally, the noise voltages on the PCB inside the enclosure due to the illumination of the EMI are calculated by using the incident fields and the radiated fields based on the reaction theorem. A direct method using the FEM is employed to validate the proposed method, and good agreement between the results obtained by the two methods is observed.